1. Field of the Invention
The present invention relates to a semiconductor device (typically transistor) and a manufacturing method thereof, and more particularly the present invention belongs to a technical field of a display device using thin film transistors as devices. That is, the present invention belongs to a technical field relating to a display device represented by a liquid crystal display device or an electroluminescence display device or the like, a technical field relating to a sensor represented by a CMOS sensor or the like, or a technical field relating to all semiconductor devices mounting other semiconductor integrated circuits.
2. Description of the Related Art
Recently, the development of a liquid crystal display device and an electroluminescence display device which integrates thin film transistors (TFTs) on a glass substrate has been in progress. Either one of these display devices constitutes one of the semiconductor devices which are characterized in that the thin film transistors are built in the glass substrate using a thin film forming technique, and liquid crystal elements or electroluminescence (hereinafter simply abbreviated as EL) elements are formed on various circuits which are constituted of thin film transistors thus functioning as a display device.
A circuit constituted of the thin film transistors has some surface irregularities and hence, in forming the liquid crystal elements or the EL elements on the circuit, an inorganic insulation film(inorganic insulating film), an organic insulation film or the like which is formed by a spin coating method is used as a leveling film. The inorganic insulation film formed by the spin coating method is also referred to as an SOG (Spin-On-Glass) film. Each pixel formed on a display part of the display device includes a pixel electrode therein, and the pixel electrode is connected to a thin film transistor through a contact hole formed in the above-mentioned leveling film.
However, it has been known that the SOG film has water permeability and water retentivity and hence, use of SOG film as an interlayer insulation film is limited. That is, although the SOG film may be used as a material which compensates for stepped portions in the technical field of LSI, there is no possibility that the SOG film is used as the interlayer insulation film (interlayer insulating film). This is because that when the SOG film is used as the interlayer insulation film, the SOG film allows moisture or the like to pass therethrough so that there is a fear that the moisture or the like adversely affects electronic characteristics (particularly leaking current or the like) of a transistor formed below the SOG film.
Further, even with an interlayer insulation film having a laminar structure which sandwiches the SOG film between other insulation films formed by a plasma CVD (Chemical Vapor Deposition) method or the like, for example, the SOG film is exposed in a cross section of a contact hole (also referred to as “via”) so that there arises a problem of a so-called poisoned via which forms a moisture supply source and erodes wiring or the like.
The present invention has been made in view of the above-mentioned problems and it is an object of the present invention to provide, in manufacturing a display device using an SOG film as an insulation film for leveling surface irregularities attributed to semiconductor devices (typically thin film transistors), a technique which can solve problems on water permeability and water retentivity of the SOG film and can achieve the enhancement of stability of operational performance of the display device. Further it is also an object of the present invention to achieve the enhancement of image qualities of the display device in combination.